"I am shocked at the latest reports from Syria that large numbers of civilians have again been killed in a totally unjustified assault by Syrian security forces on the town of Hama," Ashton said in a statement.

Of those killed on Sunday, a hundred were shot as the security forces stormed Hama, said activists.

"This attack and the continuing crackdown in other Syrian cities is even more unacceptable coming on the eve of the holy month of Ramadan," Ashton added.

"The Syrian army and security forces have the duty to protect citizens, not to massacre them indiscriminately.

"Those responsible for these attacks must be held accountable and brought to justice," the statement added.